May 14, 2012
(CORDIS) — The Filchner-Ronne Ice Shelf, a major Antarctic ice shelf in the Weddell Sea, may start to melt rapidly and cease to act as a barrier for ice streams draining the West Antarctic Ice Sheet. This is the new stark warning from a group of EU-funded climate researchers.
Using various model calculations, the team successfully demonstrated that rising air temperatures above the south-eastern Weddell Sea could trigger large ice masses to slide into the ocean within the next six decades.
The research is supported by the ICE2SEA (‘Estimating the future contribution of continental ice to sea-level rise’) project, which is backed by nearly EUR 10 million under the ‘Environment’ Theme of the EU’s Seventh Framework programme (FP7).
Writing in the journal Nature, the team, made up of scientists from Germany and the United Kingdom, contend the commonly held assumption that ice shelves in the Weddell Sea would be immune to the direct effects of global warming due to its peripheral location. Until now, many experts in the field have believed that the consequences of global warming for Antarctica would be noticeable primarily in the Amundsen Sea, the western part of Antarctica.
Lead study author, Dr Hartmut Hellmer from the Alfred Wegener Institute for Polar and Marine Research (AWI), comments on the urgent need to start turning our attention eastwards: ‘The Weddell Sea was not really on the screen because we all thought that unlike the Amundsen Sea, its warm waters would not be able to reach the ice shelves. But we found a mechanism which drives warm water towards the coast with an enormous impact on the Filchner-Ronne Ice Shelf in the coming decades.’
Dr Hellmer describes ice shelves as ‘corks in the bottles for the ice streams behind them’ and explains the important role they play: ‘[Ice shelves] reduce the ice flow because they lodge in bays everywhere and rest on islands.’ He warns: ‘If, however, the ice shelves melt from below, they become so thin that the dragging surfaces become smaller and the ice behind them starts to move.’
The study models show that the warmer air will thin the currently solid sea ice in the southern Weddell Sea and make it more fragile and prone to movement over the coming decades. An inflow of warmer water beneath the Filchner-Ronne Ice Shelf will melt the ice from below and change the dynamic of the ice streams. The team’s calculations show that a hydrographic front in the southern Weddell Sea that has so far prevented warm water from getting under the ice shelf will disintegrate by the end of this century.
The team’s calculations are based on atmospheric projections from the British Met Office Hadley Centre in Exeter. These included information on future wind patterns and temperature in Antarctica.
Jürgen Determann, also from the AWI, comments: ‘We expect the greatest melting rates near the so-called grounding line, the zone in which the ice shelf settles on the sea floor at the transition to the glacier. At this point, the Filchner-Ronne Ice Shelf is melting today at a rate of around 5 metres per year. By the turn of the next century, the melt rates will rise to up to 50 metres per year. If the high melting rates are completely compensated by inland ice flow, this loss in mass would correspond to an additional rise in global sea level of 4.4 millimetres per year.’
The latest estimates based on remote sensing data show that the global sea level rose for the period from 2003 to 2010 at a rate of 1.5 millimetres per year, due to melting of glaciers and ice shelves. This rise is in addition to the 1.7 millimetres per year due to thermal expansion of the oceans.
The ICE2SEA project brings together researchers from 24 research institutes across Belgium, Chile, Denmark, Finland, France, Germany, Iceland, Italy, the Netherlands, Norway, Poland and the United Kingdom. The global aim of the project is to successfully decode the interactions between ice and climate, and in turn facilitate more precise predictions about the effects of melting ice on sea levels.
Another paper published in the journal Nature Geoscience this week also warns of the danger posed to the stability of the Antarctic Ice Sheet.
This team, led by Martin Siegert from the University of Edinburgh in the United Kingdom, surveyed the thickness of the Institute and Möller ice streams, both of which feed the Filchner-Ronne Ice Shelf. The researchers set out to determine the underlying landscape.
Their findings reveal a steep reverse slope and a large sub-glacial basin upstream of where the West Antarctic Ice Sheet meets the Weddell Sea. Unfortunately the bed is fairly smooth, with little in the way of any features or ‘pinning points’ that could stop the retreat of the ice sheet in its tracks.
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